This slipped under my radar but it deserves attention. Three weekends ago, an item on the BBC's Sunday Politics programme began with the presenter, Jo Coburn, saying that "Sunday Politics can exclusively reveal new research claiming that there is a direct link between advertisements for prostitutes in the back of newspapers and sex trafficking."

That surprised me. I haven't previously come across any research making "a direct link", though I did report in November 2010 that Scotland Yard had accepted it as fact by writing a warning letter to 170 London newspaper editors.

It said they could be held criminally liable if they ran ads for sex establishments that turn out to be linked to human trafficking, exploitation or the proceeds of crime.

This threat didn't deter most publishers from continuing to carry the ads, presumably because they were confident that a causal link between the ads and trafficking could not be proved.

And, incidentally, no editor or publisher has been arrested or charged since that warning was issued.

So does the "new research" at last show an incontrovertible link? According to the Sunday Politics guest, Mary Honeyball, a London Labour MEP who commissioned the research, it does just that. But her statements on the programme were less than convincing.

She came up with an eye-opening statistic: 94.6% of women in London who work in sex industry are migrants (Can that be true?) She then admitted that not all of them have been trafficked, prompting Coburn to ask: "So what's the proportion?" Honeyball didn't say.

And the answer? There isn't a figure beyond a 2010 Scotland Yard estimate (itself disputed). The report is interesting and not without merit, but it is not much more than a collation of previous research.

It provides no new figures and justly concedes the fact by stating in the preamble:

"The evidence base of research on this issue is complex, contested and incomplete, both due to the politically and socially challenging nature of the issues at stake; and to the practical and methodological difficulties inherent in researching criminalised and often stigmatised areas of social life."

There is lots of circumstantial evidence, which adds up to an inference well short of proof. I do not doubt, and have said so before, that almost all the sex adverts in newspapers are placed by brothels or by individual prostitutes. Publishers would have to be extraordinarily naive to believe otherwise.

In that sense, newspaper publishers cannot be other than aware that they are promoting prostitution. (I absolve editors because they don't have control of advertising policy).

That said, it is a giant leap to claim that publishers are responsible, by publishing the ads, for the trafficking of women. There are no reliable statistics about the numbers of women trafficked into Britain.

Though there cannot be any doubt that it happens, the scale of the problem is unknown and probably wildly exaggerated (See Nick Davies's 2009 report).

I suspect that some trafficked women have been coerced into working in brothels that have been advertised in newspapers. I also suspect that when non-British women working in brothels are arrested, many of them claim they have been trafficked when, in fact, they came here of their own volition.

Of course, I don't know anything for certain - and neither does anyone else, including "the authorities."

People who should know better tend to bandy around figures with little proof. For example, on the Sunday Politics show, two other guests quoted figures that don't bear too much scrutiny.

Catherine Stephens, representing the International Union of Sex Workers, said "about 5%" of women working in the sex industry are trafficked. Really? How does she know? It's another guesstimate.

And a London Labour MP, Seema Malhotra, said confidently that local papers get £44m in revenue from sex ads. Do they? That figure first emerged in 2007 in an "audit" carried out for the Central Office of Information. It may have been wrong then - it was described as being "approximate" - and it's very unlikely to be true now.

Since then, some publishers have stopped running the ads. In July 2008, Newsquest (which has a US parent, Gannett) banned ads for sexual services. And, in September 2011, Archant decided not to run sex adverts in two of its daily titles but it has continued to do so in some of its London weeklies (a fact, incidentally, the Honeyball research overlooks).

None of what I've written should be taken to suggest that I am either condemning or condoning prostitution. I am simply stating the reality of a situation bedevilled by a lack of genuine information.